Wave and tidal flushing in a near-equatorial mesotidal atoll

Costa, Mirella Borba Santos Ferreira; Macedo, Eduardo Cavalcante de; Valle‐Levinson, Arnoldo; Siegle, Eduardo

doi:10.1007/s00338-016-1525-x

Cited by 14 publications

(18 citation statements)

References 31 publications

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“…Smaller, but still significant exchanges through the channels driven at tidal timescales were more pronounced in the vicinity of the southern channel; the topography at the northern channel entrance (i.e., flood‐tide delta‐like feature) resulted in comparatively less flushing. The significance of channels acting as conduits for exchange in atolls has been highlighted in a number of previous studies (Callaghan et al, ; Costa et al, ; Dumas et al, ; Kench, ; Kraines et al, ). However, to our knowledge, this is the first study whereby the interaction of regional tidal characteristics with an atoll is a primary flushing driver.…”

Section: Discussionmentioning

confidence: 96%

“…Therefore, the connectivity of an atoll to the open ocean often depends strongly on how flows interact with submerged reef flats and/or channel systems or breaks in the reef rim. There have been a number of hydrodynamic studies in different atoll settings that have described circulation driven by a combination of wave, wind, and tidal processes (Andréfouët et al, ; Callaghan et al, ; Costa et al, ; Dumas et al, ; Kraines et al, ; Rogers et al, ; Tartinville et al, ). These studies have primarily been conducted in wave‐dominated environments, where waves play a dominant role in at least some parts of the reef system.…”

Section: Introductionmentioning

confidence: 99%

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Hydrodynamics of a Tidally Forced Coral Reef Atoll

2018

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The hydrodynamics of a tidally forced semi-enclosed coral reef atoll (North Scott) at the edge of the continental shelf of northwestern Australia were investigated by combining field observations and numerical modeling. The observations revealed that the spring tidal range outside the atoll reaches 4 m, and as the water level drops below mean sea level, the reef rim surrounding the shallow (~10-15 m) lagoon becomes exposed. During this time, the lagoon can only exchange with the open ocean through two narrow channels, resulting in highly asymmetric water levels and velocities that were most pronounced during spring tide. On average, the ebb tide duration was~2 hr longer than the flood, with rapid flood velocities in the channel reaching 2 m/s. We applied an unstructured grid model Delft3D-Flexible Mesh to simulate the atoll hydrodynamics and were able to replicate the asymmetric water levels and complex velocities in the lagoon. The results revealed that at higher tidal stages, a dominant momentum balance exists between the pressure gradient (established by the propagation of the tide on the shelf) and the local flow acceleration of water throughout the interior of the atoll. At lower tidal stages, which coincided with a reversal of the offshore tidal pressure gradient, the lagoon became isolated from offshore dynamics and all momentum terms were negligible. This resulted in a tidally averaged residual westward flow within the lagoon that drove an asymmetric flushing pattern within the atoll, which we propose would be a common flushing mechanism within other tide-dominated atolls worldwide.Key Points:• The hydrodynamics of a tide-dominated atoll reef system were assessed with field observations and numerical modeling • The semi-enclosed atoll morphology and large tidal range resulted in highly asymmetric water levels, velocities, and residual flows • A residual east-west flow, caused by interactions between the phasing of the ocean tide and lagoon water levels, dominated flushingSupporting Information:• Supporting Information S1

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Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Hydrodynamics of a Tidally Forced Coral Reef Atoll

2018

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“…Breach and flooding has also been reported as an important mechanism in modifying reef islands, either causing localized shoreline erosion (Sheppard, ) or aiding to infilling the central depression through sediment transport from the reef flat to the site of deposition at the island sink, which can result in vertical and horizontal accretion (Hamylton and East, ). Whereas progressive changes in the central depression can be caused by channel migration, rapid morphological changes in the central depression are likely triggered by extreme events, which for the Rocas Atoll consist of energetic ocean swells occurring simultaneously with high spring tides (Costa et al, ). Therefore, despite the decadal growth observed at Farol Island, the island stabilization depends also on the dynamics of the central depression.…”

Section: Discussionmentioning

confidence: 99%

“…Substantial morphological changes were also observed in the central depression (mud bay), marked by the central ridge breach (Figures 4a and 4b), which increased the area of the central depression. Despite the central depressions of the reef islands being recognized as low-wave energy areas, at Farol Island they are dominated by an active tidal channel with strong flow driven by the inherent mesotidal Rocas atoll system (Costa et al, 2017). During ebb tides, the entire volume of water outflows through the tidal channel and the central depression emerges during low tides.…”

Section: Response To Incident Wave Energymentioning

confidence: 99%

Planimetric and volumetric changes of reef islands in response to wave conditions

Costa

Macedo

Siegle

2017

Earth Surf Processes Landf

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Reef islands are morphologically dynamic features located on atolls and platform reefs that are very sensitive to wave‐induced processes on different timescales. The planform morphological evolution of reef islands is widely described; however, the mechanisms of the volumetric variations in response to wave energy are still poorly documented. To assess their multitemporal vertical and horizontal mobility, we performed a series of synchronous measurements of the volumetric changes and incident wave energies at two reef islands and a shingle bank at the Rocas Atoll in the South Atlantic Ocean. The results show the differences in the magnitudes and locations of the sediment mobility between the reef islands. Whereas one island remained stable on all timescales, with only small volumetric changes concentrated at its extremities, the other island (Farol Island) showed high mobility, especially during the energetic northern swell season. The gross volumetric change reached 10.03 × 103 m3 (5% of the total island volume) on a daily timescale; however, on a seasonal scale, the gross erosion was compensated by the gross accretion, indicating a cyclical seasonal pattern. Moreover, the observed volumetric changes induced by the waves on both daily and seasonal timescales did not result in large shoreline displacements. However, long‐term oceanward erosion and substantial lagoonward accretion were observed at Farol Island on a decadal scale, resulting in a pronounced change in its planform morphology. This appears to be promoted by at least three sediment transport pathways induced by waves at the atoll, including sediment adjustment between the reef islands. Our results show that reef islands on the same atoll can have very distinct morphological behaviors on daily, seasonal and decadal scales in response to the same boundary conditions. Copyright © 2017 John Wiley & Sons, Ltd.

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“…Dampak ini tidak hanya disebabkan oleh keberadaan KALP tetapi juga oleh faktor-faktor iklim seperti El-Nino Southern Oscillation (ENSO) yang berpengaruh terhadap anomali suhu perairan secara global dan regional karena lokasi Selat Lombok adalah salah satu gerbang Arus Lintas Indonesia (ARLINDO). Signifikansi ekologis musiman dan pelepasan air tanah di bawah laut dapat memicu kematian karang (Costa et al, 2017). Variasi suhu permukaan laut antar laut dari Selat Lombok secara nyata memperkuat terjadinya peristiwa pendinginan yang jauh lebih kuat yang sangat mendorong adaptasi biota laut (Song et al, 2007).…”

Section: Dampak Keberadaan Kalp Dengan Suhu Rendah Ke Lingkungan Sekitarunclassified

Faktor Hidro-Oseanografi Terhadap Distribusi Air Tawar Bersuhu Rendah Dekat Pantai Sekitar Lokasi Keluaran Air Tanah Lepas Pantai (KALP) di Perairan Lombok Utara, Indonesia

Wisha¹,

Kusumah²

2019

OLDI

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<p><strong>The Influence of Hydro-Oceanography Factors on the Distribution of Near-shore Low-Temperature Freshwater around Submarine Groundwater Discharge (SGD) Area in the North Lombok Waters, Indonesia.</strong> North Lombok coast has lot of resources of Submarine Groundwater Discharge (SGD). The biggest discharge appeared in the Krakas Beach where cold groundwater discharge many spots might trigger anomalies in the ambient water temperature. This study was aimed at determining the distribution of the cold groundwater discharge. A field survey was conducted on March 23th -26th, 2016. Flow model and statistical analysis were employed to determine the transport pattern of temperature anomalies. Vertically, the current direction is in accordance with Ekman spiral that triggers the vertical cold groundwater distribution. The current speed during the displacement toward high tide ranges 0-0.15 cm/s which predominantly moves south-westward. During low tide, tidal current was predominantly north-eastward moving at 0-0.3 cm/s. Temperature variation around the SGD spot fluctuated following sea surface surface elevation dynamics in which these two parameters has a correlation value of 63%.</p>

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Wave and tidal flushing in a near-equatorial mesotidal atoll

Cited by 14 publications

References 31 publications

Hydrodynamics of a Tidally Forced Coral Reef Atoll

Hydrodynamics of a Tidally Forced Coral Reef Atoll

Planimetric and volumetric changes of reef islands in response to wave conditions

Faktor Hidro-Oseanografi Terhadap Distribusi Air Tawar Bersuhu Rendah Dekat Pantai Sekitar Lokasi Keluaran Air Tanah Lepas Pantai (KALP) di Perairan Lombok Utara, Indonesia

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